One method to control fuel injection for an internal combustion engine is presented in patent application No. 2005/0155578 A1. In particular, this method presents a way to control two separate injectors that can supply fuel to an individual cylinder. The method controls a port injector and an in-cylinder injector during various engine operating conditions. The port injector period of injection is defined such that it roughly agrees with the period during which the combustion/expansion stroke and exhaust stroke are done (the 360° Crank angle degree period from top dead center of compression to the top dead center of the exhaust). Depending on the engine operating conditions an appropriate point of injection time is set in the before mentioned port injector range. On the other hand, the injection period for the in-cylinder injector is defined such that injection is done during the intake stroke (the 180 crank angle degree period from the top dead center of the exhaust stroke to the bottom dead center of the intake stroke). Depending on the engine operating conditions an appropriate point of injection time is set in the before-mentioned in-cylinder injector range.
The above-mentioned method can also have several disadvantages. Specifically, the method limits the crankshaft interval over which the port injector and the in-cylinder injector may inject fuel to the cylinder. These limitations may reduce the benefit of a dual injector system, at least during certain engine operating conditions. For example, the injection limitations may reduce fuel vaporization and mixing during some conditions. Furthermore, it may be possible to lower engine emissions when fewer constraints are placed on injection timing since more opportunity exists to control in cylinder fuel kinetics.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method to control an engine during the regeneration of an exhaust gas after treatment device that offers substantial improvements.
One embodiment of the present description includes a method to control injection timing for an internal combustion engine having a plurality of injectors in at least a cylinder, the method comprising: injecting a first fuel amount to at least a cylinder of an internal combustion engine from a first injector; injecting a second fuel amount fuel to said cylinder from a second injector; and adjusting the timing between starting or ending injection of said first fuel amount, and starting or ending of said second fuel amount in response to an operating condition of said engine. This method overcomes at least some of the limitations of the previously mentioned methods.
By allowing a wide range of injection periods between two injectors supplying fuel to a cylinder, it may be possible to improve fuel mixing and engine emissions. Specifically, it may be possible to improve mixing of cylinder fuel by overlapping port and in-cylinder injection periods. During the injection overlap period the in-cylinder injection may cause fuel spray patterns to overlap, thereby increasing mixing of the two fuel sources. This may be beneficial when injecting two different types of fuel (e.g., Ethanol and gasoline) because a more homogeneous air-fuel mixture may be produced. In addition, a temperature distribution throughout the cylinder may be produced by the in-cylinder injection so that the velocity of air through the intake port may be increased while fuel is injected through an open intake valve. Furthermore, the before-method allows at least a portion of the in-cylinder injection period to enter the compression stroke. This may be useful when starting a warm engine using ethanol because the injected ethanol may have less time to enter cylinder crevasses where it may be combusted less completely.
The present description may provide several advantages. In particular, the method may be used to improve fuel mixing during engine starting or at partial engine loads. This may be especially useful when more than one type of fuel is to be combusted, ethanol and gasoline for example. In addition, the method may be beneficial because it allows in-cylinder injection to begin and end later in a cylinder cycle. For example, for engines using late intake valve opening the in-cylinder injection can overlap into the compression stroke, if desired.